Fluid bed catalytic operations such as the catalyzed cracking of hydrocarbons are well known in the art. Indeed, fluidized catalytic cracking of hydrocarbon feeds is a widely practiced commercial process.
In recent years, there has been a need in fluidized catalytic cracking operations to process heavier hydrocarbon feedstocks as well as to produce products having higher octanes. This need has been met, in part, with the development of higher activity catalysts as well as by operating the reactors at significantly higher temperatures. Unfortunately these higher activity catalysts and higher operating temperatures can lead to secondary cracking of the hydrocarbon feedstock thereby producing undesirable coke on the catalyst and unwanted light gas products.
New reactor vessels such as the so-called transfer line reactors are designed to minimize these side reactions, in effect, by minimizing the time the catalyst and hydrocarbons (feed and reaction products) spend in the reactor vessel. Converting existing reactor vessels which utilize catalyst of significant tonnage in a so-called "bed", however, to transfer line systems is quite costly and hence frequently not economically attractive. Thus there remains a need for improving existing fluid catalytic cracking reactor vessels in such a way as to minimize catalyst coking and secondary cracking of hydrocarbons therein.